The present invention relates to a magnetoresistive head for reading magnetically encoded information. In particular, the present invention relates to a magnetoresistive sensor having an improved readback characteristic.
Magnetoresistive sensors are used to read back magnetically encoded information. In a magnetoresistive sensor, a sense current is passed through a magnetoresistive element. The sense current causes a voltage drop due to a resistance of the magnetoresistive element. The presence of a magnetic field causes the resistance of the magnetoresistive element to change. This change in resistivity can be detected by measuring the voltage drop across the magnetoresistive element.
The sense current in the active region of the magnetoresistive element may be represented by a current density vector J. Additionally, the active region has a magnetization vector, M. To obtain a linear output of the magnetoresistive sensor, the magnetization vector M and the current density vector J should form an angle near 45.degree.. This arises because the output voltage is a function of the cosine squared of the angle between J and M which has a maximum slope at 45.degree..
Obtaining a 45.degree. angle between M and J is accomplished by either rotating M or rotating J with respect to the easy axis (EA) of the magnetoresistive element. The easy axis is defined as the position of the magnetization vector when all orientation influences are absent, with two rest positions being 180.degree. apart. Rotation of the magnetization vector M is achieved by applying an external magnetic field, such as a permanent magnet built into the head structure. Additionally, current carrying paths built into the head structure, coupled magnetic films, or soft adjacent layers can be used to rotate the magnetization vector M. The current density vector J typically is perpendicular to contact edges used to contact the active region of the magnetoresistive element.
Performance of magnetoresistive sensors can be determined by measuring a read sensitivity function. The read sensitivity function is a graph of sensor output obtained while a "microtrack" propagates across the surface of the head. A microtrack is a source of magnetic flux which is small in width relative to the active region of the head. A microtrack is an analytical device used to measure sensitivity of a magnetoresistive sensor. Additionally, magnetic flux enters the sensor in a direction perpendicular to the magnetization vector M. An ideal read sensitivity function would have a rectangular shape. In practice, it generally has a triangular or trapezoidal shape which will reduce track density due to offtrack interference.
A magnetoresistive sensor having an improved head sensitivity function would be an important contribution to the art.